Optical fibers twinning apparatus and process

ABSTRACT

This specification describes a twinned pair of optical fibers having two optical fibers twisted about each other axially. Also described is a fiber optics cable having at least one twinned pair of optical fibers.

BACKGROUND

Most optical fibers are made from glass, and are therefore very fragile and delicate. To protect these fibers, they are usually covered by protective layers and housed in cables. FIG. 1 shows a typical optical cable. The glass fiber 10 is surrounded by a glass cladding 11, and a buffer 12 that surrounds the cladding 11 to offer protection from the environment and to provide mechanical strength. In fibers known as tight-buffer fibers, the buffer 12 is wrapped tightly around the cladding to add some stiffness to the fiber and provide greater protection than thinner, conventional buffers. A tight-buffer increases the diameter of the fiber to about 900 microns.

A tight-buffer cable, a cross-section of which is shown in FIG. 2, typically has a plurality of tight-buffer fibers 14 stranded together around a central member 15 to form a bundle 16 of fibers. In some high fiber count cables, the bundle consists of a number of various tight buffer fiber layers. The bundle 16 is then coated with strength members 17, such as aramid yarn, which provide tensile strength to the cable. The strength members 17 are then coated with an outer jacket 18 to provide additional structural and environmental protection to the fibers 14. In some cables each tight-buffered fiber is also covered with its own strength members and jacket before the fibers are stranded together into a bundle.

Tight-buffer cables can be constructed with tight-buffer fibers in either a straight bundle or a helical bundle. In a straight bundle, the fibers are stranded together so that they run parallel to each other without winding around each other or forming a helical twist. To prevent structural and cracking problems with the optical fibers, tight-buffer cables are typically constructed by stranding the fibers in a twisted, helical bundle rather than a straight bundle. In a helically stranded bundle, the fibers are helically twisted around each other, or around a central member.

In certain helically stranded bundle constructions, the direction of the helical twist reverses direction at various points along the cable, thereby adding extra fiber length to the fiber relative to the cable length. This is done by a stranding process known as reverse oscillation lay, or SZ stranding. Cables having extra fiber length facilitate small, tight bends and have reduced stresses on the fibers during bending because the extra fiber length gives the fibers room to move and adjust to the bends. Extra fiber length also allows splicing or coupling from the cable mid-span by allowing greater lengths of the fiber to be drawn from the cable.

Helically stranding the fibers and adding extra fiber length to the cable occur during the cabling process. A conventional cabling process begins with a large machine called a strander, which has a number of payoffs for holding and dispensing lengths of fiber. It can also have a central reel or payoff that holds and dispenses the central member of the cable. As the payoffs dispense the fibers, the strander winds them around the central member, and/or each other, in a helical bundle.

The cabling process may also include a reverse oscillation lay process during stranding that periodically reverses the direction of the helical twist in order to add extra fiber length. After stranding and/or reverse oscillation lay, strength members are applied to the stranded fibers. Finally, the cabling process concludes with the jacket line where the fibers and strength members are covered with a polymer jacket, such as polyethylene.

This process of constructing fiber optic cables has several limitations, however. First, it requires using the same number of payoffs as the number of fibers to be used in the cable, since each payoff only holds one fiber. For example, to make a 24-count fiber optic cable with this process requires a strander with 24 payoffs. Although not all payoffs need to be used, these stranders do not allow construction of cables with more fibers than the number of payoffs on the strander, thereby limiting the range of use of existing equipment.

Another problem is that the fibers must undergo the reverse oscillation lay process in order to induce extra fiber length. This additional process increases the chance for larger variations of lay length, and gives less control over the oscillated lay since this process is done at the time of cabling. Furthermore, the oscillator must be capable of turning the same number of fibers as are included in the cable. For example, a 24 fiber cable requires an oscillator capable of turning 24 fibers.

Fiber optic cables produced by this process also have problems. For example, even though the reverse oscillation process induces extra fiber length, it must also be known at what points in the cable the direction of the helical twist reverses in order to be able to use the extra fiber length to splice or make connections in the cable mid-span. These reversal points are usually covered by the jacket, and therefore are difficult to locate.

Finally, the method for marking individual fibers in a conventional cable has several problems. The conventional method for marking consists of using a different colored jacket for each fiber. But this can become costly and causes delays in manufacturing. In high fiber count cables, it can also become difficult to differentiate between different shades of one color.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the apparatuses and methods described herein will become apparent from a consideration of the following detailed description, presented in conjunction with the drawings, in which:

FIG. 1 shows an exploded view of a typical 900 micron tight-buffer fiber.

FIG. 2 shows a cross-section of a typical tight-buffer cable;

FIG. 3 depicts a twinned pair of optical fibers, as described herein; and

FIG. 4 shows a side view of a bundle of helically stranded twinned fibers.

FIGS. 1-4 illustrate specific aspects of the principles described herein and are a part of the specification. Together with the following description, the Figures demonstrate and explain the apparatus, products and methods described herein and are views of only particular—rather than complete—portions of such.

SUMMARY

This specification describes a twinned pair of optical fibers having two optical fibers twisted about each other axially. Also described is a fiber optics cable having at least one twinned pair of optical fibers.

DETAILED DESCRIPTION

The following description provides specific details of embodiments of the invention. The skilled artisan will understand, however, that embodiments of the invention can be practiced without employing these specific details. Indeed, embodiments of the invention can be practiced by modifying the described methods and products and can be used in conjunction with apparatus and techniques conventionally used in the industry. For example, the following description provides an apparatus and method for twinning and stranding optical fibers and constructing tight-buffer fiber optic cables. The methods described herein can be modified, for example, for construction of loose-tube cables. The methods could also be modified to twist three or more fibers rather than two. Indeed, those skilled in the art will recognize other uses and adaptations of the present methods and products.

The present specification describes a method and apparatus for constructing a tight-buffer cable using fewer payoffs than the number of fibers in the cable. The method and apparatus also eliminate the need for a reverse oscillation lay process to induce extra fiber length in a cable. The product described herein also provides a more efficient and effective means of marking and identifying fibers in a cable. By utilizing the apparatus in conjunction with the methods described herein, a manufacturer of both copper and fiber cables can use existing copper manufacturing equipment in a more efficient manner.

These tasks are performed by using twinned pairs of optical fibers in fiber optic cables. To construct cables comprising twinned pairs, two optical fibers are first twisted together to form a twinned pair. Usually a modified copper wire twinner is used to form the twinned pair. The twinned pair is then collected onto a payoff, thereby allowing each payoff to hold at least two optical fibers, rather than just one. The twinned pair is then paid off into a strander, where it is stranded and jacketed to create a fiber optic cable.

Twinned optical fibers add many benefits to the fibers and to the overall cable construction. First, twinned fibers, and thus twinned pairs, have better strength and mechanical properties than do single, untwinned fibers. By twisting two fibers about each other, stresses from bends or other stresses imparted on a particular fiber are distributed throughout the fiber because a portion of one fiber will be on the outside of the bend, while another portion will be on the inside of the bend. Thus, the stresses will distribute evenly over the length of the twist.

Second, twinned pairs also provide a more efficient method of managing and marking the inventory of fibers. When twinned pairs are used in a cable, only one fiber in each pair, and thus one out of every two fibers, need have an independent color or marking. Each fiber is instead identified by the combination of its color and the color of its corresponding twinned fiber. For example, a twinned pair could be made of a blue and a white fiber, another pair orange and white, and another pair red and white. Thus, fewer colors are needed in order to mark individual fibers in a cable, thereby saving processing time and money.

Finally, twinned pairs also allow two fibers to be collected on one payoff, because the twinned pair acts as a single strand. This allows a strander, oscillator or other cabling equipment to use fewer payoffs than the number of fibers in the cable, resulting in a more efficient and wider range of use of the equipment. For example, a strander having only 12 payoffs can be used to create a cable having up to 24 fibers.

One of the products described herein includes a twinned pair having two fibers twisted about each other, as shown in FIG. 3. The twinned pair lay length L is the distance along the cable required for the fiber to make one complete twist. The twinned pair lay length has a significant effect on the performance of the optical fibers as related to optical transmission. Too little length between twists will degrade the optical performance, and too much length between twists will cause the twinned pair to fall apart during subsequent production. The twinned pair lay length should also not cause the fibers to bend tighter than their minimum bend radius.

In one embodiment, the twinned pair lay length is constant along the length of the pair. In another embodiment, the twinned pair lay length varies along the length of the twinned pair. Twinned pairs can also be made from any type of fiber, such as 900 micron tight-buffer fibers. The twinned fibers can also be buffered fibers each having a strength member and an outer jacket.

This specification also describes two twinned pairs twinned together to form a quad. In another aspect, one fiber can be twinned with a twinned pair, forming a triplet. Those of skill in the art will understand that other modifications and variations of a twinned pair not herein disclosed can also be made.

Another product herein described includes a cable having twinned pairs. FIG. 4 shows one embodiment in which a cable has only twinned pairs. In another embodiment, a cable comprises at least one twinned pair, and in another embodiment a cable comprises at least one twinned pair and at least one untwinned fiber. Cables with twinned pairs provide a number of advantages over cables having only single, untwinned fibers. First, twinned pairs add extra fiber length to the fibers relative to the cable. This results because the length of one fiber needed to create a twinned pair is longer than a single, untwinned fiber used in the same length of cable.

Second, in cables comprising twinned pairs, the extra fiber length for each fiber can vary from twinned pair to twinned pair because the twinned pair lay length of each pair can be varied. The ability to have varied extra fiber length among pairs allows cables to be more bend resistant. For example, in a single cable design, it may be desirable to have multiple layers of twinned pairs stranded together to form a larger fiber count cable. In this configuration, it can be beneficial to have a twinned pair lay length of the outer pairs different than that of the inner pairs.

Third, cables having helically stranded twinned pairs do not require a reverse lay configuration in order to induce extra fiber length. One aspect of the product includes a cable having at least one twinned pair helically stranded without a reverse lay configuration. Because a twinned pair alone induces extra fiber length, it is not necessary for the helical twist to reverse directions. Thus, mid-span splicing and coupling of fibers can be done at any point along the cable because there is no point where the helical twist reverses direction. In another aspect, the cable includes a twinned pair helically stranded with a reverse lay configuration in order to induce even more extra fiber length.

Fourth, cables comprising twinned pairs have reduced and distributed stresses on the fibers. Twinned fibers distribute stresses throughout the fiber while the strength members and outer jacket of the cable absorb much of the stress resultant to bending. These outer layers also give strength to the cable, protect the fibers from crushing and other impacts, absorb some of the tension in pulling the cable, and protect the fibers from the environment.

This specification describes cables wherein at least one twinned pair is helically stranded. Helical stranding distributes and reduces the stresses on the cable in addition to the stress distribution provided by a twinned pair. In another aspect this specification describes a cable having at least one twinned pair stranded in a straight bundle configuration, rather than a helically stranded bundle. In this aspect the extra fiber length and stress distribution is provided solely by the twinned pair.

Finally, cables comprising twinned fibers can have a high fiber count because fewer payoffs are needed. For example, a cable that comprises from about 24 to about 48 fibers needs only about 12 to about 24 payoffs.

The present specification also describes an apparatus for twinning two optical fibers together. In one aspect, a conventional copper wire twinner, which is a device that twists two copper wires around each other, can be modified to twin two optical fibers together. Conventional copper wire twinners typically have two payoffs, each holding a length of copper wire; sheaves that act as pulleys to guide the wires through the device; and a takeup for collecting a twinned pair of wires. The payoffs and the takeup each have independent tension control for regulating wire tension, and the twinner has controls for regulating the twinner rotational speed and the line speed at which the wires pass through the twinner. Due to the fragile nature of optical fibers the sheaves, payoffs and takeup, as well as twinner operating standards, can be modified for use with optical fibers.

In one aspect, the sheaves of the twinner are modified to have a radius equal to or greater than the specified minimum bend radius of the optical fibers. Typical copper wire twinners have sheaves with small bend radii, and therefore could cause structural and optical damage to the optical fibers. They can also have a greater tolerance for copper fines and burrs on the sheave, but since optical fibers are made from glass the fibers may be damaged by fines and burrs. The sheaves of the modified twinner are therefore cleaned and fines and burrs are removed to meet optical fiber processing requirements.

In another aspect, the twinner payoffs are also modified to facilitate the use of tight-buffer fiber payoffs. Fiber payoffs meet fiber processing requirements and ensure that the fibers do not bend more than the minimum bend radius allows, but they have an arbor hole that is a different size than the conventional payoff arbor hole. Thus, the twinner may be modified to use fiber payoffs by using pintle adapters to allow the fiber payoffs to fit the twinner pintle. In another aspect, the twinner may be modified for use of fiber payoffs by adapting the pintle sizes to fit the fiber payoff arbor holes.

In another aspect the twinner take-up reel is also modified to allow use of reels compatible with subsequent process steps, such as fiber payoff reels used in the stranding process. Such reels also have a different arbor hole size, and can thus be modified by adapting the pintle size to fit the arbor hole of the fiber take-up reel. In another aspect, the twinner can be modified by using a pintle adapter to allow the fiber take-up reel to fit with the twinner pintle.

In addition to modifying the sheaves, payoffs and takeup, twinner operational standards can also be modified in order to protect the optical fibers and maintain their optical integrity. In one aspect the tension in the fibers is set so that it does not exceed the maximum specified tension for the fibers. The payoffs of the modified twinner have independent tension control, as does the takeup reel, and each can be used to set the correct tension.

The twinner is also adjusted to produce a twinned pair lay length that does not violate the minimum bend radius of the individual fibers. Shorter twinned pair lay lengths result in tighter bends, and therefore the minimum bend radius may be violated. The twinned pair lay length can be varied by adjusting the rotational speed, or by adjusting the line speed. In another aspect, the twinned pair lay length can be set by adjusting the speed of the twinner takeup without increasing the speed of the twinner rotation.

The present specification also describes a cabling system for manufacturing a fiber optic cable. In one aspect the system includes a twinner modified for twinning optical fibers, a strander and a jacket line. In this system, two individual optical fibers are fed into the twinner, where they are twisted into a twinned pair. The twinned pair is then collected onto a payoff, which then dispenses the twinned pair as the twinned pair is stranded by the strander. Finally, the stranded twinned pair passes through a jacket line where it is extruded with a polymer jacket.

In constructing a cable with multiple fibers, this system allows fewer payoffs to be used than the number of fibers to be stranded in the cable because each payoff can hold at least two fibers when they are twinned together. This system also allows a manufacturer of both copper and fiber cable products to use existing copper manufacturing equipment in a more efficient manner by utilizing modified copper twinners for twinning optical fibers.

One of the methods herein described includes a method for inducing extra fiber length into a cable. As described above, extra fiber length can be induced by helically stranding optical fibers in a reverse lay configuration using a reverse oscillation lay process, but this method creates complications in the jacketing process. The method for inducing extra fiber length dispenses with the need for an oscillation process, and also eliminates related jacketing complications.

In one aspect of this method, extra fiber length can be induced by twinning two optical fibers and using a twinned pair in a cable. The presence of the twist imparts extra fiber length to the fibers relative to the cable. In another aspect, the extra fiber length can be induced by twinning together two optical fibers and stranding the twinned pair using a strander. In one aspect, the twinned pair is helically stranded. In yet another aspect, the twinned pair is helically stranded with a reverse lay configuration. The reverse lay configuration also helps induce extra fiber length, and although it is not necessary, it allows the addition of greater amounts of extra fiber length when it is coupled with a twinned pair.

This specification also describes a method for twinning optical fibers together. The twinning method allows two optical fibers to be twisted about each other, as shown in FIG. 3. In one aspect, two fibers are twinned by inserting them into a conventional copper wire twinner modified for use with optical fibers and using the modified twinner to twist the fibers about each other. In this aspect the payoff and takeup tension are set so that the maximum specified tension of the fiber in the process is not exceeded. The twinned pair lay length setting of the twinner is also set so that the twinned fibers do not violate the minimum bend radius. The fibers may also be twinned by hand, or by wrapping one fiber around another fiber that is held still. Those skilled in the art will recognize that various means may be employed to twin two fibers together.

Another method described herein is a method for manufacturing a fiber optic cable. The method for manufacturing generally comprises (1) twinning at least two optical fibers together to form a twinned pair, (2) stranding at least one twinned pair, and (3) covering the stranded fibers with strength members and a jacket. This method of manufacturing a cable allows for more efficient use of existing equipment, and allows high-fiber count cables to be constructed more quickly and efficiently. Another aspect of the method includes stranding any combination of twinned pairs and untwinned fibers. Another aspect of the stranding includes a reverse oscillation lay process.

In another aspect, the method for manufacturing comprises using half as many payoffs as the number of fibers to be stranded. In another aspect, the method comprises using fewer payoffs than the number of fibers to be stranded. This is possible because at least one twinned pair, and thus two fibers, can be held on each payoff.

It is to be understood that the above-described arrangements of the methods, apparatus and products are only illustrative of the application of the principles described herein. Modifications of the components may be devised by those skilled in the art without departing from the spirit and scope of the principles described herein, and the appended claims are intended to cover such modifications and arrangements. 

1. A twinned pair of optical fibers, wherein two optical fibers are twisted about each other axially.
 2. The twinned pair of claim 1, having a twinned pair lay length that maintains said fibers at or above their minimum bend radius.
 3. The twinned pair of claim 1, wherein said lay length varies along the length of the twinned pair.
 4. A cable, comprising at least one twinned pair of optical fibers.
 5. The cable of claim 4, further comprising an untwinned optical fiber.
 6. The cable of claim 4, wherein said at least one twinned pair is helically stranded.
 7. The cable of claim 6, wherein said at least one twinned pair has a reverse oscillation lay configuration.
 8. A cable, comprising two or more twinned pairs of optical fibers, wherein said twinned pairs provide two or more different twinned pair lay lengths.
 9. A twinner, comprising: two fiber payoffs having independent tension control; rotational speed control; line speed control; a takeup with independent tension control; and sheaves that have a radius greater than or equal to the minimum bend radius of the fiber being processed and that are cleaned to fiber processing requirements.
 10. The twinner of claim 9, wherein said twinner comprises a conventional copper wire twinner modified for use with optical fibers.
 11. A twinner, comprising a conventional copper wire twinner modified for use with optical fibers, wherein said twinner is modified by: replacing copper wire payoffs with fiber payoffs; replacing a copper wire takeup with a fiber reel; and using sheaves that have a radius greater than or equal to the minimum bend radius of the fibers being processed and that are cleaned to fiber processing requirements.
 12. The twinner of claim 11, wherein said twinner is further modified by: setting the tension to not exceed the maximum specified tension for the fibers being twinned; and setting the twinned pair lay length to not violate the minimum bend radius for said fibers.
 13. A method for inducing extra fiber length into an optical fiber cable, comprising: using a twinned pair of optical fibers in a cable.
 14. A method for inducing extra fiber length into an optical fiber cable, comprising: twinning together two optical fibers; collecting a twinned pair onto a single payoff; stranding said twinned pair; and jacketing said stranded twinned pair.
 15. The method of claim 14, wherein said stranding comprises reverse oscillation lay stranding.
 16. A method for twisting optical fibers together, comprising: inserting at least two optical fibers into a twinner modified for use with optical fibers; and using said twinner to twist said at least two fibers about each other.
 17. A method for manufacturing a fiber optic cable, comprising: twinning two fibers together to form a twinned pair; stranding at least one twinned pair; and jacketing said at least one stranded twinned pair.
 18. The method of claim 17, wherein said stranding is helical stranding.
 19. The method of claim 17, further comprising inducing extra fiber length by reverse oscillation lay.
 20. A method for manufacturing a fiber optic cable, comprising: using fewer payoffs than the number of fibers to be stranded; stranding at least two optical fibers; and jacketing the stranded fibers.
 21. A system for manufacturing a fiber optics cable, comprising: a copper wire twinner modified for use with optical fibers; a strander; and a jacket line.
 22. A quad of optical fibers, comprising: two twinned pairs twisted about each other axially.
 23. A triplet of optical fibers, comprising: a twinned pair of optical fibers and a single, untwinned fiber twisted about each other axially.
 24. A method for managing optical fibers in a cable, comprising: using a plurality of twinned pairs of optical fibers in a cable; and marking the fibers of said twinned pairs with one or more colors, wherein more than one fiber is marked with a particular color, but wherein no two fibers marked with the same color have identically marked corresponding twinned fibers.
 25. A method for managing optical fibers in a cable, comprising: using a plurality of twinned pairs of optical fibers in a cable, each pair having a first fiber and a second fiber; and marking each fiber of each twinned pair; wherein the combination of the marking of said first fiber and the marking of said second fiber of one twinned pair is not duplicated by another twinned pair in said cable. 